/Engine/Source/Runtime/Engine/Public/StereoRenderTargetManager.h
Updates viewport for direct rendering of distortion. Should be called on a game thread.
void UpdateViewport ( bool bUseSeparateRenderTarget, const class [FViewport](API\Runtime\Engine\FViewport) & Viewport, class [SViewport](API\Runtime\Slate\Widgets\SViewport) * ViewportWidget )